1. Field of the Invention
The present invention relates to a flow diffuser with an elongate discharge nozzle which can be used as a 90xc2x0 elbow in piping systems. The flow diffuser can be located in or immediately upstream of a measurement station or custody transfer station to improve measurement accuracy. The flow diffuser promotes laminar fluid flow and reduces pulsation in gas pipelines.
2. Description of the Prior Art
In piping systems, orderly or streamlined flow is desirable. When a fluid passes through a conventional valve or a 90xc2x0 turn at a conventional elbow, the fluid flow becomes disorderly or turbulent. This turbulent fluid does not return to a streamlined or laminar flow for at least 40-50 pipe diameters downstream of an elbow. (Assuming that the downstream piping is axially aligned with the outlet of the valve or elbow and has the same inside diameter.)
Turbulence can be caused by a number of factors including, but not limited to, boundary layer separation, sometimes referred to as flow separation, vortices, pressure waves and/or cavitation. Turbulence in pipe systems often causes noise, vibration, erosion and/or stress cracking. Reduction of turbulence is desirable in valves, at elbows and in piping systems generally, both upstream of gas or liquid measurement and downstream of compressor stations.
Turbulence also causes a drop in fluid pressure. Each time a fluid flows through a valve or elbow, there is an incremental drop in fluid pressure between the inlet and the outlet. In transmission pipelines, pressure drops are undesirable. If the fluid pressure drops low enough, additional pumping stations may be required. In any event, adding pressure to the fluid in the pipeline increases transportation costs. Because the elbow of the present invention reduces turbulence, it has less of a pressure drop when compared with conventional 90xc2x0 elbows.
Elbow induced turbulence has been recognized and addressed by a number of prior art designs including the vanes of U.S. Pat. No. 5,197,509 and No. 5,323,661 which are located upstream from an elbow. These vanes impart rotation to the fluid as it passes through the elbow to reduce downstream turbulence. Others have considered the deleterious effects of elbow induced turbulence and have included rotation vanes both upstream and downstream of an elbow as described in U.S. Pat. No. 5,529,084. These inventions seek to create non-turbulent or laminar flow after fluid passes through a conventional elbow.
The use of curved vanes to influence fluid flow for various reasons is not a new concept. In U.S. Pat. No. 1,570,907, a plurality of vanes were used in a locomotive to separate water from steam.
Japanese Patent Application Serial Number Sho58 (1983)-13899 was filed on Jan. 31, 1983 by Yamatake Honeywell Co. Ltd. for a Valve Seat for Control Valve and Its Manufacturing Method. This prior art valve discloses a comb-like cylinder equipped with multiple teeth of rectangular cross-section formed as one piece with the ring-shaped valve seat. These teeth may be formed at the lower end of the valve seat on the outlet side or may be formed at both the upper and the lower end of the valve seat. The manufacturing method of the valve seat occurs sequentially. First, multiple slits are formed in the radial direction on the cylindrical wall joined to the ring-shaped valve seat as one piece. Then the rectangular teeth forming these slits are twisted plastically (i.e., by exerting torsional moments at the tip of the teeth large enough to cause permanent deformation) so that each slit is oriented in the direction of the fluid flow at its respective position. Because of the rectangular shape of these teeth, they promote turbulence instead of encouraging laminar flow.
In some piping systems, granular or particulate material will quickly wear out a conventional elbow. One way to address this problem is by increasing the radius of curvature of the elbow to about 10 pipe diameters. However, this is not an entirely acceptable solution, especially in areas where space is at a premium. There have been many attempts to solve this erosion problem, including the use of inserts in the elbow, the insert being a disposable item intended to be replaced when it wears out. Examples of this type of replaceable insert in an elbow can be found in the following U.S. Pat. No. 1,357,259; No. 2,911,235; No. 3,942,684; and No. 5,590,916.
Other proposed solutions to this erosion problem include a circular pocket off the elbow. This pocket accumulates a certain quantity of the particulate material which serves as a pad to absorb the blow of the subsequent material to reduce the erosive effects thereof as shown in U.S. Pat. No. 4,387,914 and No. 5,060,984.
Conventional valves are also known to create turbulence and a pressure drop between the inlet and the outlet. Robert H. Welker, the inventor herein and the inventor of U.S. Pat. No. 5,730,416, has developed various approaches to deal with valve induced turbulence. In another patent, U.S. Pat. No. 5,769,388, Mr. Welker has developed a plurality of vanes and passageways in the valve to reduce turbulence. The apparatus shown in U.S. Pat. No. 5,769,388 has certain shortcomings because of the short discharge nozzle which tapered at an included angle of approximately 12xc2x0. There is still a need to reduce turbulence in elbows, in valves and in piping systems in general.
In a gas pipeline, pulsation is normally caused by reciprocating compressors and can be caused to a lesser degree by certain types of check valves. Pulsation in a gas pipeline is typically the result of the pistons in a reciprocating compressor pushing the gas out in distinct pressure waves which may move five to ten miles downstream of a pumping station. Pulsation is never desirable.
Liquid pipelines reduce pulsation by installing pulsation dampeners, many of which commercially available. Pulsation in a liquid pipeline can cause failure. The present invention should reduce pulsation in a liquid pipeline.
The present invention should also reduce pulsation in gas pipelines. Pulsation in gas pipelines can cause measurement error at custody transfer stations and other measurement installations. Pulsation pressure waves require sensitive instruments to be detected.
The traditional solution to reduce pulsation in a gas pipeline is a pulsation dampener, for example, those produced by Burgess Manning Corp. of Cisco, Tex. 76437.
Prior art pulsation dampeners typically cause at least a 15 psi permanent pressure drop in the pipeline. The present invention will reduce pulsation in a gas pipeline with only a nominal pressure drop, i.e., less than 5 psi.
The present invention can be used as a 90xc2x0 elbow in piping systems to reduce turbulence and pulsation. The elbow, sometimes referred to as a flow diffuser, is connected to an inlet conduit and an outlet conduit. The flow diffuser includes a convenient top entry design allowing access to the removable flow conditioner. Downstream of the flow conditioner is a transition zone, and an elongate tapered discharge nozzle. Fluid flows from the inlet conduit into the flow diffuser, through the flow conditioner, the transition zone, and the elongate tapered discharge nozzle to the outlet conduit.
The removable flow conditioner includes a plurality of vanes defining a plurality of passageways to guide the fluid flow from the inlet into the transition zone and elongate tapered discharge nozzle. The purpose of the guide vanes is to reduce asymmetric flow, swirling, jetting and other turbulence and to promote a symmetric velocity profile and/or laminar flow as the fluid turns a 90xc2x0 corner. In gas pipelines, the vanes also reduce pulsation. The flow conditioner can be fabricated as a replaceable part to facilitate maintenance of the flow conditioner. One way to develop a symmetric velocity profile is the design of the vanes and passageways in the replaceable flow conditioner. The width of the outlets from the passageways may be non-uniform in order to promote streamlined flow.
After the flow diffuser has been fabricated, it is desirable to test and align the flow conditioner for maximum effectiveness before it is shipped to the field. This alignment process may only require minor adjustments to properly orient the flow conditioner relative to the discharge nozzle. After the adjustments have been made the flow conditioner will need to be locked in place. In some embodiments, the adjustment mechanism and the locking mechanism are separate structures. In one alternative embodiment with opposing set screws, the adjustment mechanism also locks the flow diffuser in place. In some situations it may also be desirable to further calibrate/adjust the flow diffuser in tandem with a meter after both have been installed in the field.
The flow diffuser can be used in piping systems with liquids, gases, and steam, as well as two-phase flow, three-phase flow, and dry particulate and granules.